Chromatography is a well-established and valuable technique in both preparative and analytical work as well as in purification generally. Typical industrial chromatography apparatus has an upright housing in which a bed of packing material, usually particulate, rests against a permeable retaining layer. Fluid mobile phase enters through an inlet e.g at the top of the column, usually through a porous, perforated, mesh or other restricted-permeability layer, moves through the packing bed and is taken out at an outlet, typically below a restricted-permeability layer.
Changing the bed of packing material, because it is spent or in order to run a different process, is an arduous task particularly with big industrial columns which can be hundreds of litres in volume. The existing bed has usually become compacted and difficult to remove. The housing must be dismantled, the compacted packing mass disrupted and then removed. Furthermore, the new bed must be very evenly packed if the column is to be effective: the fresh material must be added carefully while maintaining a flow of liquid. Usually the apparatus must be kept clean, particularly with biological products where high system sterility may be needed for weeks or even months. One small contamination can be disastrous.
Conventionally, many hours have been needed to change the spent packing in a big column.
GB-A-2258415 describes a column which can be packed and unpacked without taking it apart, using special supply and discharge valves in the top and bottom plates of the housing. The packing supply valve has a spray nozzle which can be retracted into the top plate, with the spray openings closed by a seal on the plate, or advanced to project into the column bed space, freeing the openings for a slurry of packing material to be pumped in. The discharge valve has an advanceable nozzle with radially-directed spray openings at its enlarged head, positioned coaxially within a wider bore of the bottom plate. When retracted, the head fits in the bore to seal itself and the bore. To empty the column, the nozzle is advanced and buffer liquid pumped through it. The advanced nozzle head breaks up the packed medium and the pumped-in buffer carries it out through the larger bore, now opened.
There are difficulties in maintaining long-term sanitary conditions with these valve assemblies.